My custom 3.5" cold air intake

[L_RAO]

In referencing this classic DIY article:

http://www.teamdelsol.com/technical/howto/coldAirIntake/default.html

I wanted to build my own custom 3.5 intake. I haven't gathered all the parts I need yet, so this post will be part 1, and will be continuously updated.

Parts needed/that I will use:

1. Silicone coupler (3.5" --> 3.0") to mate with the throttle body
2. Silicone coupler for the fender well turn
3. Velocity stack
4. Conical air filter
5. 180 degree U bend, 3.5" mandrel bent pipe (16 gauge mild steel)
6. (3) cans of high-temperature paint: (1) primer, (2) white, and (3) clear coat
7. (2) rubber grommets for the vacuum ports

So here are some pics from testing fitting.

 

[Prospeed]

Looking good man! Hope to test it out soon! =)

 

[96cxt]

Why not use aluminum? Its alot lighter.

When measuring is it 3.5" ID or OD?

Nice write up.

 

[L_RAO]

Why not use aluminum? Its alot lighter.

When measuring is it 3.5" ID or OD?

Nice write up.

My research determined that mild steel has better heat soak characteristics than aluminum. With respect to weight, we might be talking about a pound when all is said and done.

3.5" is the OD.

Thanks. I have to give you most of the credit for your intake manifold work as my inspiration. Still looking forward to your CAI pics.

 

[greenberet]

In case you haven’t seen them, there are good DIY articles on AutoSpeed.com as well: http://autospeed.com/cms/search/index.html?keywords=airbox+filter+intake&x=0&y=0

I look forward to seeing what you build!

 

[gt_nfr]

Are you Planning to weld the pipe or just use rubber couplings for the turns?

 

[L_RAO]

I will use rubber couplings, including a 3.5"-->2.75" reducer at the throttle body. Welding it into a one-piece unit would make it impossible to install (i.e., you need to have the flexibility to orient the pipe that runs through the fender).

Does anyone in So Cal have access to a bandsaw or a similar cutting device? I need to cut my U pipe into a couple of pieces.

 

[Timeless1]

I will use rubber couplings, including a 3.5"-->2.75" reducer at the throttle body. Welding it into a one-piece unit would make it impossible to install (i.e., you need to have the flexibility to orient the pipe that runs through the fender).

Does anyone in So Cal have access to a bandsaw or a similar cutting device? I need to cut my U pipe into a couple of pieces.

L_Rao, i would recommend welding it so that it will be one solid piece & will sound superb. I will be doing my own too soon & there will be a way to snake that 3.5" pipe thru that fender wall (might have to dolly it to open it up a little).

For cutting metal, might want to try a metal cut off saw, they're not that expensive, between $69 to $99.
I got mine from Harbor Frieght.

BTW, I had to modify that B-line one, reason is i didn't like that crimp on the larger hoses, so had to put back the stock coupler to the throttle body & cut a 3" pipe & expand one end to fit the stock couple & now i'm good to go. You might want to consider this too & not waste money on that after market coupler. Keep us updated.

 

[NSX1145]

Apexi makes a great 3" Air Filter

 

[L_RAO]

Yes, but since I'm using a 3.5" bellmouth (velocity stack), the base needs to be about 6" in order to surround the bellmouth.

 

[L_RAO]

So here are some more test fitment pics:

1. The bellmouth

2. The bellmouth attached to the "long" pipe (I also have a 3.5"-->2.75" reducing coupler on the TB end).

 

[96cxt]

Is that going to go through the fender?

 

[L_RAO]

Yes, there's a 2nd pipe (that pic was just a test fitting of the bellmouth) that will run through the fender.

This particular pipe needs to be cut again.

 

[Moses]

Updates?

 

[L_RAO]

So the original filter/velocity stack combo that I have won't fit in the fender. It will, however, make for a beautiful short ram intake.

I did buy another filter that does fit; however, I was told by AEM that it did have an integrated velocity stack. IT DOESN'T. In talking to the industry leader in velocity stacks, I was told that for a 3.5" ID, the v-stack needs to have an OD of 6" in order to properly "feed" the piping.

So, I will build & test both: a true-cold air (no v-stack), vs. a short-ram with properly designed & integrated velocity stack.

 

[RYU]

So the original filter/velocity stack combo that I have won't fit in the fender. It will, however, make for a beautiful short ram intake.

I did buy another filter that does fit; however, I was told by AEM that it did have an integrated velocity stack. IT DOESN'T. In talking to the industry leader in velocity stacks, I was told that for a 3.5" ID, the v-stack needs to have an OD of 6" in order to properly "feed" the piping.

So, I will build & test both: a true-cold air (no v-stack), vs. a short-ram with properly designed & integrated velocity stack.

In terms of the short-ram, it would be great to try it w/ the hatch open and closed for a bit (i.e. warm air or cool air)

Love these test!

 

[L_RAO]

In terms of the short-ram, it would be great to try it w/ the hatch open and closed for a bit (i.e. warm air or cool air)

Love these test!

The short-ram will be as "cold" as possible; I will have the Cantrell Concepts intake scoop in the fender and it will be fed by a super fan blowing at 60 mph to simulate real-world driving.

 

[L_RAO]

So I finally got around to fitting the new AEM filter (it fits in the fender, but it does NOT have an integrated velocity stack).

I also got the piping that sits in the fender sized properly.

So...

My short-ram is DONE.

My cold-air is waiting on the "long" pipe (from throttle body to fenderwell).

 

[greenberet]

If you’re going to have a Cantrell intake scoop and a silicone coupler, could you also carry out a third test - the OEM airbox with the Cantrell scoop and silicone coupler?

 

[L_RAO]

The Cantrell scoop already meets/couples with an OEM coupler.

 

[greenberet]

I should have been clearer which coupler I meant. I meant “1. Silicone coupler (3.5" --> 3.0") to mate with the throttle body”. Since the exit of the OEM airbox has an internal diameter of 3.42", the 3.5" coupler should fit pretty well over the outside and it may allow a smoother airflow than the OEM bellows does.

 

[Hapa88]

In case you haven’t seen them, there are good DIY articles on AutoSpeed.com as well: http://autospeed.com/cms/search/index.html?keywords=airbox+filter+intake&x=0&y=0

I look forward to seeing what you build!

Some good information here.. I found this article the most interesting where discusses intake pipe length and how it can affect power by as much as 7%.

http://autospeed.com/A_107749/cms/article.html

This got me thinking as to how did you come up with the pipe length (I assume it was just governed by the length to the fender) and what made you decide to go with the large 3.5" tubing?

 

[96cxt]

So I finally got around to fitting the new AEM filter (it fits in the fender, but it does NOT have an integrated velocity stack).

I also got the piping that sits in the fender sized properly.

So...

My short-ram is DONE.

My cold-air is waiting on the "long" pipe (from throttle body to fenderwell).

What size is that filter? What is the surface area?

 

[L_RAO]

Some good information here.. I found this article the most interesting where discusses intake pipe length and how it can affect power by as much as 7%.

http://autospeed.com/A_107749/cms/article.html

This got me thinking as to how did you come up with the pipe length (I assume it was just governed by the length to the fender) and what made you decide to go with the large 3.5" tubing?

Pipe length is a function of available space. In both cases (short-ram and cold-air) I made the pipe as long as possible. Most formulas suggest about 32" of piping length for a 3.5" OD pipe, but I was only able to utilize approximately 12" (short-ram) and 25" (cold-air).

As to piping diameter, I'm going off of what the B-series guys have figured out empirically, which is that 3" isn't big enough and 4" is too big.

 

[L_RAO]

What size is that filter? What is the surface area?

Per K&N formulas, I needed 64 square inches of filtering area.

The short-ram uses a filter that is approximately 128 square inches of filter area. K&N says that going with a larger filter is not detrimental to performance, it simply increases servicing intervals.

The cold-air uses an AEM filter that is 64 square inches of filter area.